1. Field of the Invention
This invention relates to rectangular waveguides and more particularly to ridge waveguides of the type in which provision is made for a sealed window or in other words a partition-wall which is transparent to electromagnetic energy but impervious to gases and moisture.
2. Description of the Prior Art
When a wide band of operating frequencies is desired for a rectangular waveguide provided with a sealed window, an attractive possibility consists in adopting a ridge waveguide. It is known that, in a device of this type, one or more longitudinal internal ridges are formed in the waveguide walls, primarily in order to increase transmission bandwidth by lowering the cutoff frequency. A waveguide corresponding to this definition and provided with a window has already been disclosed in U.S. Pat. No. 3,860,891 issued on Jan. 14, 1975, and which is a continuation in part application of U.S. Ser. No. 102,590, filed Dec. 30, 1970, now abandoned. This patent describes a thick dielectric window with a small transition zone on each side in which the internal ridges are suppressed and in which the cross-section of the waveguide has a height equal to the maximum height of the waveguide section which contains the dielectric material of the window. Unfortunately, this window-type waveguide has an operating frequency bandwidth which is limited to one octave and is liable to produce parasitic resonances or ghost modes arising from the thickness of the dielectric.